In recent years, by-wire control, i.e., control by an electrically operated actuator such as, for example, brake-by-wire, throttle-by-wire, or steer-by-wire has been adopted in control apparatuses for vehicles in order to give a detailed control in order to cope with fine control. Various sensors are required for such control apparatuses so that when a sensor or sensors are in disorder serious accidents will occur due to inability to control. Also, unstable control will give uneasy feeling to drivers. Accordingly, diagnostic tests of sensors are carried out. When it is determined that a sensor is abnormal, safety back-up operation is carried out. Japanese Laid-open Patent Application No. 2003-200822 discloses a method for diagnosing abnormality of sensors, in which method the sensors have each a self diagnosis function and diagnostic signals are obtained from the sensors at predetermined timing.
The technology disclosed in Japanese Laid-open Patent Application No. 2003-200822 relates to a self diagnosis method for a hydraulic sensor in a brake control system. In this conventional technology, the brake control system is equipped with a plurality of sensors, of which only one sensor has a self diagnosis function to perform self diagnosis. The only one sensor is a hydraulic pressure sensor of high importance.
The timing at which self diagnosis is started is set to a time immediately before the start of control or a point in time when a certain condition that does not adversely affect the braking control is established.